1. Field of the Invention
The present invention is related to continuous envelope feeders of the type adapted to be used in conjunction with printers or labelers which place information on the envelope. More particularly, the present invention relates to novel apparatus for stripping a single envelope from a stack of envelopes without jamming or feeding two envelopes.
2. Description of the Prior Art
U.S. Class 271, Subclass 2 contains sheet feeding or delivering apparatus/envelopes and contains patents dating before 1900 which teach envelope feeders. Prior art envelope feeders have recognized the problem that it is impossible to stack envelopes horizontally, vertically or otherwise in a magazine and to remove a single envelope in every instance. The prior art devices are capable of operating correctly most of the time but not all of the time. The friction that occurs between a stack of envelopes in a magazine is effected by pressure, temperature, humidity and also the thickness of the envelope as well as the surface texture. When these conditions combine it is possible to feed one envelope mechanically and have the adjacent envelope adhere thereto causing a double feed of envelopes. None of the prior art in the aforementioned Class 271, Subclass 2 deal directly with this problem nor does it offer a hundred percent solution. For example, U.S. Pat. No. 2,267,574 is directed to an envelope feeding mechanism which opens the flap of the envelope so as to permit pinch rolls to pull the flap and trailing envelope out of a magazine. By opening a single flap from the bottom envelope the pinch rolls are only capable of grasping one envelope from the magazine at a time. Even this teaching has no provision for preventing the closed envelope stacked on top of the open envelope from adhering to the envelope being fed into the pinch rolls and double feeding of envelopes is possible. Moreover, there are numerous modern day printers such as carriage printers and laser printers which require that the flap of the envelope be closed in order to fit properly into the feed mechanism of the printer and devices such as this teaching will require an additional mechanism to close the flap before being used in such printers.
As a second example U.S. Pat. No. 2,521,237 teaches an envelope printing press which has a self-contained rotary print roller. A vertical magazine of envelopes with flaps down is mounted adjacent to the roll printer and a second roll having spring fingers at its outer edges engages under the end portions of the flap of the envelope positioned in the magazine so as to pull the envelope out of the magazine and into the gap formed between the rotary print roll and the pinch roll. Again, if adverse conditions occur the envelope being pulled from the magazine will also carry a second envelope into the printing press. Another example of a printing press feeder is provided in U.S. Pat. No. 1,724,199 which employs a sliding plate. The slide plate is designed to slip under the flap of an envelope loaded in a magazine with its flap down. To assure that the slide plate does not slide past an envelope and does select at least one envelope a plurality of vacuum holes are provided opposite the loose flap so as to separate the loose flap from the envelope to allow the slide plate to feed one envelope. Under adverse conditions more than one envelope can be fed into the printing press.
Advances in adhesive technology have substantially overcome the problem of flaps on envelopes self-sealing due to minor changes in humidity or as a result of being stacked vertically. However, modern technology has provided the user with standard business envelopes that have six layers of thickness at the center portion and only two layers of thicknesses over the major portion of the envelope. In addition to non-uniformity of thickness of the envelope and its adhesive layers, the material from which the envelope is made can vary substantially in thickness so as to cause major problems with the feeding apparatus designed to continuously feed envelopes into printers.
It is conservatively estimated that in the United States alone the sales of printers for computing use including laser printers, dot matrix printers, daisy wheel printers and thermal printers will exceed 7 million units in the 1987 alone. While there are numerous manufacturers of laser printers, only one manufacturer of laser printers manufactures an envelope feeder. While there are many manufacturers of envelope feeding equipment only a few recognized quality manufacturers of envelope feeding equipment provide envelope feeders for laser printers. One of the problems associated with a laser printer is that the envelope must be oriented in a proper direction for insertion into the laser printer and in most cases the envelope must be provided in a ready or standby state to be fed into the laser printer when the laser printer establishes that another envelope is needed.
It would be extremely desirable to provide an economical and predictably repeatable envelope feeder which may be adapted for use with laser printers as well as other types of printers without the requirement for expensive adaptive hardware.